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I'm not sure how it's happened but for some reason when using a shared internet connection on my iMac (OS X Lion) all internet traffic is now blocked from being sent to my other devices. However things like streaming radio do work.

How can I figure out what's blocking the port used for internet over WiFi?

ifconfig:

lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
     options=3<RXCSUM,TXCSUM>
     inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1 
     inet 127.0.0.1 netmask 0xff000000 
     inet6 ::1 prefixlen 128 

gif0: flags=8010<POINTOPOINT,MULTICAST> mtu 1280

stf0: flags=0<> mtu 1280

en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
     options=2b<RXCSUM,TXCSUM,VLAN_HWTAGGING,TSO4>
     ether 00:1e:c2:15:e2:2a 
     media: autoselect
     status: inactive

en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
     ether 00:1e:c2:a3:f7:11 
     inet6 fe80::21e:c2ff:fea3:f711%en1 prefixlen 64 scopeid 0x5 
     inet 10.0.2.1 netmask 0xffffff00 broadcast 10.0.2.255
     inet 169.254.254.145 netmask 0xffff0000 broadcast 169.254.255.255
     media: autoselect
     status: active

fw0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 4078
     lladdr 00:1f:5b:ff:fe:0a:2a:5c 
     media: autoselect <full-duplex>
     status: inactive

vnic0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
       options=3<RXCSUM,TXCSUM>
       ether 00:1c:42:00:00:08 
       inet 10.211.55.2 netmask 0xffffff00 broadcast 10.211.55.255
       inet6 fe80::21c:42ff:fe00:8%vnic0 prefixlen 64 scopeid 0x7 
       inet6 ::1 prefixlen 64 
       media: autoselect
       status: active

vnic1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
       options=3<RXCSUM,TXCSUM>
       ether 00:1c:42:00:00:09 
       inet 10.37.129.2 netmask 0xffffff00 broadcast 10.37.129.255
       inet6 fe80::21c:42ff:fe00:9%vnic1 prefixlen 64 scopeid 0x8 
       inet6 ::1 prefixlen 64 
       media: autoselect
       status: active

ppp0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1500
      inet 10.136.35.37 --> 10.99.195.231 netmask 0xffffff00 

utun0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1380
       inet6 fe80::21e:c2ff:fe15:e22a%utun0 prefixlen 64 scopeid 0xa 
       inet6 fd00:6587:52d7:10c5:21e:c2ff:fe15:e22a prefixlen 64
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whats the output of ifconfig in a termnial when your wifi is connected? –  Shutupsquare Jan 26 '12 at 12:11
    
Added all the results for ifconfig above but I think you only need en1 for Wifi? –  EddyR Jan 27 '12 at 5:06
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2 Answers

Check your DNS settings. Most streaming apps use IP-only addresses.

Head to Network prefs, and make sure you're not setup with something custom, like a home router that isn't accessible.

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Your output from ifconfig for en1 shows 2 inet (IP) addresses which is a little confusing and will require more troubleshooting.

The first IP address shown on en1 is 10.0.2.1 which may or may not be right, you would have to check the wireless interface on the computer sharing the connection. I am a little unclear as to whether the iMac is broadcasting its internet connection to share with others or if it's one of the devices that is receiving a shared connection from another.

Either way, unless the sharing system is acting as a DHCP server to hand out IP addresses, chances are you need to configure each device to have an individual IP address.

But then there is this very unusual issue -

en1 also has an IP of 169.254.254.145 which is a result of not getting an IP address from from a DHCP server and is self-assigning a link-local or APIPA address which can not be used when you are trying to access the Internet because the address cannot be routed.

computernetworking.about.com (APIPA):

Definition: A feature of Microsoft Windows [and most modern operating systems], APIPA [link-local] is a DHCP failover mechanism for local networks. With APIPA, DHCP clients can obtain IP addresses when DHCP servers are non-functional.
...
When a DHCP server fails, APIPA allocates IP addresses in the private range 169.254.0.1 to 169.254.255.254. Clients verify their address is unique on the network using ARP. When the DHCP server is again able to service requests, clients update their addresses automatically.

Here is what I recommend to resolve the issue. Hopefully I understood the issue clearly but this is with the understanding that the iMac is the system that is supposed to broadcast the Internet connection and you are connecting other devices to it via WiFi:

Check the configuration of the wireless network interfaces on all devices. If you are using the 10.0.2.x scheme - set the iMac to 10.0.2.1 and the others to 10.0.2.2 through 10.0.2.254 just ensuring that you don't have two devices with the same IP. You will want to set the netmask to 255.255.255.0 on the wireless interface on the iMac as well as all the devices you want to connect - on everything but the iMac, set the default gateway to 10.0.2.1 . Just to be safe, I would manually set the DNS server IP's to 208.67.222.222 and 208.67.220.220 (openDNS) to make sure all your bases are covered.

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